Almost Prime.cpp

/*
https://ide.geeksforgeeks.org/1CnAZPvX7p
*/
//Bitset Sieve
#include<iostream>
#include<bitset>
#include<algorithm>
#include<vector>
using namespace std;
#define ll long long
const int n=10000000;
vector<int>primes;
bitset<10000005>b;//making an array of bits of size 10000005.
void sieve()
{  b.set();//sets all the bits as 1
    b[0]=b[1]=0;
    for(ll i=2;i<=n;i++)
    { if(b[i])// if the bit is set bit then push it into vector primes
        {   primes.push_back(i);
            for(ll j=i*i;j<=n;j=j+i)//mark all its multiple as 0 except the number itself
            {b[j]=0;}
        }
    }
}
int main()
{sieve();//calling the sieve function
int j,l,c=0,s=0;
cin>>l;
for(j=3;j<=l;j++)
{c=0;
    for(int i=0;i<=3000;i++)
{
    if(j%primes[i]==0)
    c++;
    //cout<<primes[i]<<" ";
    
}
if(c==2)
s+=1;
//printing the prime array
}
cout<<s<<"\n";
return 0;
}